[NFR] Support igbinary as a cache frontend

igbinary is a drop-in replacement for PHP's serialize()/unserialize() functions.

igbinary is faster than PHP's serializer (provided that `igbinary.compact_strings=Off`) and its output is usually smaller (which could be a good advantage if you have to keep a lot of (large) data).

Plus, http://www.niden.net/2011/11/fast-serialization-of-data-in-php-how.html mentions igbinary and therefore it would be good to support it in Phalcon :)